Copolymer, organic solar cell using the same and manufacturing method thereof

ABSTRACT

Disclosed herein are a 3,6-carbazle-containing copolymer, an organic solar cell comprising the copolymer in an organic material layer including a photoactive layer, and a method for fabricating the organic solar cell.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure relates to a novel copolymer, an organic solarcell comprising the same and a method for fabricating the organic solarcell.

2. Description of the Prior Art

Since the possibility of solar cells based on organic copolymers wasfirst shown by Heeger at the University of California, Santa Barbara(UCSB), in 1992, there have been many studies thereon. Such solar cellsinclude heterojunction thin film devices comprising a mixture of anorganic copolymer, which absorbs light, with a C60 or C70 fullerenederivative which has a very high electron affinity. These heterojunctionthin film devices comprise a transparent positive electrode made ofindium tin oxide (ITO) and a negative electrode made of a metal such asAl, which has a low work function.

The photoactive layer comprising the organic copolymer absorbs light toform electron-hole pairs or excitons. The electron-hole pairs move tothe interface between the copolymer and the C60 or C70 fullerenederivative at which they are separated into electrons and holes. Then,the electrons move to the metal electrode, and the holes move to thetransparent electrode, thereby generating electrodes.

Currently, the efficiency of organic copolymer thin-film solar cellsbased on organic copolymers reaches 7-8% (Nature Photonics, 2009, 3,649-653).

However, the efficiency of the organic copolymer solar cell is still lowcompared to the maximum efficiency (about 39%) of solar cells based onsilicon. Thus, the development of organic polymer solar cells having ahigher efficiency is required.

Korean Patent Laid-Open Publication No. 10-2010-0111767 discloses aconductive copolymer comprising 2,7-carbazole in the main chain, and anorganic solar cell comprising the same. According to the disclosure ofthe above patent publication, the conductive copolymer comprising2,7-carbazole in the main chain improves light absorption and holemobility to improve the efficiency of the solar cell.

However, there is a problem in that it is not easy to improve opticalefficiency, because the mobility of holes is relatively lower than themobility of electrons, despite the use of 2,7-carbazole.

PRIOR ART DOCUMENTS Patent Documents

-   Korean Patent Laid-Open Publication No. 10-2010-0111767

Non-Patent Documents

-   Macromolecules 2011, 44(7), 1909-1919-   Nature Photonics, 2009, 3, 649-653-   B. Nicolas, M. Alexandre, M. Leclerc, Adv. Mater. 19, 2295-2300-   Y. Human, A. Solyman, I. Ahmed, W. C. Darren, K. James, L. G.    David, J. Mater. Chem. 21, 13649-13656

SUMMARY OF THE INVENTION

It is an object of the present disclosure to provide an organicsemiconductor material, which can exhibit excellent electricalproperties thanks to its high hole mobility and has high photovoltaicconversion efficiency, and an organic solar cell comprising the same.

To achieve the above object, in one aspect, the present disclosureprovides a copolymer comprising a first unit represented by thefollowing formula 1 and at least one unit different from the first unit,wherein the first unit is present in an amount of greater than 0 mole %and 45 mole % or less based on the total moles of monomers constitutingthe copolymer:

whereino and p are each an integer ranging from 0 to 3;R_(a) and R_(b) are the same or different and are each independentlyselected from the group consisting of hydrogen, deuterium, a halogengroup, a nitrile group, a nitro group, an imide group, an amide group, ahydroxyl group, a substituted or unsubstituted alkyl group, asubstituted or unsubstituted cycloalkyl group, a substituted orunsubstituted alkoxy group, a substituted or unsubstituted aryloxygroup, a substituted or unsubstituted alkylthioxy group, a substitutedor unsubstituted arylthioxy group, a substituted or unsubstitutedalkylsulfoxy group, a substituted or unsubstituted arylsulfoxy group, asubstituted or unsubstituted alkenyl group, a substituted orunsubstituted silyl group, a substituted or unsubstituted boron group, asubstituted or unsubstituted alkylamine group, a substituted orunsubstituted aralkylamine group, a substituted or unsubstitutedarylamine group, a substituted or unsubstituted heteroarylamine group, asubstituted or unsubstituted aryl group, a substituted or unsubstitutedfluorenyl group, a substituted or unsubstituted carbazole group, and asubstituted or unsubstituted heterocyclic group containing at least oneheteroatom selected from among N, O and S, or adjacent two of R_(a) andR_(b) may form a condensed ring; andR₁ is selected from the group consisting of hydrogen, deuterium, ahalogen group, a nitrile group, a nitro group, an imide group, an amidegroup, a hydroxyl group, a substituted or unsubstituted alkyl group, asubstituted or unsubstituted cycloalkyl group, a substituted orunsubstituted alkoxy group, a substituted or unsubstituted aryloxygroup, a substituted or unsubstituted alkylthioxy group, a substitutedor unsubstituted arylthioxy group, a substituted or unsubstitutedalkylsulfoxy group, a substituted or unsubstituted arylsulfoxy group, asubstituted or unsubstituted alkenyl group, a substituted orunsubstituted silyl group, a substituted or unsubstituted boron group, asubstituted or unsubstituted alkylamine group, a substituted orunsubstituted aralkylamine group, a substituted or unsubstitutedarylamine group, a substituted or unsubstituted heteroarylamine group, asubstituted or unsubstituted aryl group, a substituted or unsubstitutedfluorenyl group, a substituted or unsubstituted carbazole group, and asubstituted or unsubstituted heterocyclic group containing at least oneheteroatom selected from among N, O and S.

In another aspect, the present disclosure provides a copolymercomprising a first unit represented by the following formula 1, a secondunit represented by the following formula 3 and a third unit representedby the following formula 4:

whereino, p, q and r are each an integer ranging from 0 to 3;s and t are each an integer ranging from 0 to 4;R₁ and R″ are the same or different and are each independently selectedfrom the group consisting of hydrogen, deuterium, a halogen group, anitrile group, a nitro group, an imide group, an amide group, a hydroxylgroup, a substituted or unsubstituted alkyl group, a substituted orunsubstituted cycloalkyl group, a substituted or unsubstituted alkoxygroup, a substituted or unsubstituted aryloxy group, a substituted orunsubstituted alkylthioxy group, a substituted or unsubstitutedarylthioxy group, a substituted or unsubstituted alkylsulfoxy group, asubstituted or unsubstituted arylsulfoxy group, a substituted orunsubstituted alkenyl group, a substituted or unsubstituted silyl group,a substituted or unsubstituted boron group, a substituted orunsubstituted alkylamine group, a substituted or unsubstitutedaralkylamine group, a substituted or unsubstituted arylamine group, asubstituted or unsubstituted heteroarylamine group, a substituted orunsubstituted aryl group, a substituted or unsubstituted fluorenylgroup, a substituted or unsubstituted carbazole group, and a substitutedor unsubstituted heterocyclic group containing at least one heteroatomselected from among N, O and S;R_(a), R_(b) and R₆ to R₁₁ are the same or different and are eachindependently selected from the group consisting of hydrogen, deuterium,a halogen group, a nitrile group, a nitro group, an imide group, anamide group, a hydroxyl group, a substituted or unsubstituted alkylgroup, a substituted or unsubstituted cycloalkyl group, a substituted orunsubstituted alkoxy group, a substituted or unsubstituted aryloxygroup, a substituted or unsubstituted alkylthioxy group, a substitutedor unsubstituted arylthioxy group, a substituted or unsubstitutedalkylsulfoxy group, a substituted or unsubstituted arylsulfoxy group, asubstituted or unsubstituted alkenyl group, a substituted orunsubstituted silyl group, a substituted or unsubstituted boron group, asubstituted or unsubstituted alkylamine group, a substituted orunsubstituted aralkylamine group, a substituted or unsubstitutedarylamine group, a substituted or unsubstituted heteroarylamine group, asubstituted or unsubstituted aryl group, a substituted or unsubstitutedfluorenyl group, a substituted or unsubstituted carbazole group, and asubstituted or unsubstituted heterocyclic group containing at least oneheteroatom selected from among N, O and S, or adjacent two of R_(a),R_(b) and R₆ to R₁₁ may form a condensed ring.

In still another aspect, the present disclosure provides an organicsolar cell comprising: a first electrode; a second electrode oppositethe first electrode; one or more organic material layers interposedbetween the first and second electrodes and including a photoactivelayer, wherein one or more of the organic material layers comprise thecopolymer comprising the first unit of formula 1.

In yet another aspect, the present disclosure provides a method forfabricating an organic solar cell, the method comprising the steps of:preparing a substrate; forming a first electrode on a region of rearsides of the substrate; forming on the first electrode an organicmaterial layer comprising the copolymer including the first unit offormula 1; and forming a second electrode on the organic material layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graphic diagram showing a comparison of charge mobilitybetween 3,6-carbazole-containing copolymers and 2,7-carbazole-containingcopolymers.

FIG. 2 is a graphic diagram showing current-voltage curves for organicsolar cells of Examples 2 to 4 and Comparative Examples 1 and 2.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the present disclosure will be described in detail.

The present disclosure provides a copolymer comprising a first unitrepresented by formula 1 and at least one unit different from the firstunit.

As used herein, the term “unit” means the polymerized form of arepeating monomer unit in the copolymer.

The first unit of formula 1 contains a substituted or unsubstituted3,6-carbazole group. An organic solar cell comprising the copolymerincluding the first unit has high charge mobility compared to an organicsolar cell comprising a 2,7-carbazole-containing copolymer, and thefirst unit of formula 1 contributes to the stability of the copolymer.

FIG. 1 is a graphic diagram showing a comparison of charge mobilitybetween 3,6-carbazole-containing copolymers and 2,7-carbazole-containingcopolymers.

In one embodiment of the present disclosure, the first unit of formula 1is preferably present in an amount of greater than 0 mole % and 45 mole% or less based on the total moles of monomers constituting thecopolymer.

In another embodiment, the content of the first unit of formula 1 is0.1-30 mole % based on the total moles of the monomers. In still anotherembodiment, the content of the first unit of formula 1 is 0.5-20 mole %based on the total moles of the monomers. In yet another embodiment, thecontent of the first unit of formula 1 is 0.5-15 mole % based on thetotal moles of the monomers. In another further embodiment, the contentof the first unit of formula 1 is 1-10 mole % based on the total molesof the monomers.

In the 3,6-carbazole-containing copolymer, a nitrogen atom is conjugatedto the main chain to stabilize holes and increase the mobilities ofholes and electrons, so that, hole mobility and electron mobility in theorganic solar cell comprising the copolymer can be balanced. Thus, thepresent disclosure provides an organic semiconductor material, which canexhibit excellent electrical properties thanks to the balance betweenhole mobility and electron mobility and has high photovoltaic conversionefficiency, and an organic solar cell comprising the same.

Conventional 2,7-carbazole-containing copolymers do not appear toexhibit excellent electrical properties, because no nitrogen atom is notconjugated to the main chain.

In contrast, if the content of the first unit of formula 1 in thecopolymer comprising the first unit of formula 1 is 45 mole % or lessbased on the total moles of monomers constituting the copolymer, areduction in the optical absorption of the copolymer, which results fromthe relatively low absorbance of the carbazole group, can be minimized.In addition, in this case, a copolymer having a suitable molecularweight can be prepared.

In one embodiment of the present disclosure, the unit different from thefirst unit in the copolymer includes at least one electron acceptor.

In one embodiment of the present disclosure, the electron acceptor ispresent in an amount of greater than 0 mole % and 50 mole % or lessbased on the total moles of monomers constituting the copolymer.

In another embodiment of the present disclosure, the unit different fromthe first unit in the copolymer includes at least one electron acceptorand at least one electron donor.

In still another embodiment of the present disclosure, the unitdifferent from the first unit in the copolymer includes at least twoelectron acceptors and at least one electron donor.

Examples of the substituents of the above formulas will be describedbelow, but are not limited thereto.

In the present disclosure, the alkyl group may be a straight orbranched-chain alkyl group, and the number of carbon atoms thereof ispreferably 1 to 20, but is not limited thereto. Specific examples of thealkyl group include, but are not limited to, methyl, ethyl, propyl,isopropyl, butyl, t-butyl, pentyl, hexyl and heptyl groups.

In the present disclosure, the alkenyl group may be a straight orbranched-chain alkenyl group, and the number of carbon atoms thereof ispreferably 2 to 40, but is not limited thereto. Specific examples of thealkenyl group include, but are not limited to, aryl-substituted alkenylgroups, such as stylbenzyl and styrenyl groups.

In the present disclosure, the alkoxy group may be a straight, branchedor cyclic chain alkoxy group. The number of carbon atoms of the alkoxygroup is preferably 1 to 25, but is not limited thereto. Specificexamples of the alkoxy group include, but are not limited to, methoxy,ethoxy, n-propyloxy, iso-propyloxy, n-butyloxy and cyclopentyloxygroups.

In the present disclosure, the cycloalkyl group preferably contains 3 to60 carbon atoms, but is not limited thereto. Particularly preferredexamples of the cycloalkyl group include cyclopentyl and cyclohexylgroups.

In the present disclosure, the halogen group may be fluorine, chlorine,bromine or iodine.

In the present disclosure, the aryl group may be monocyclic, and thenumber of carbon atoms thereof is preferably 6 to 60, but is not limitedthereto. Specific examples of the aryl group include, but are notlimited to, monocyclic aromatic groups, such as phenyl, biphenyl,triphenyl, terphenyl or stilbene groups, and polycyclic aromatic groups,such as naphthyl, anthracenyl, phenanthrenyl, pyrenyl, perylenyl,tetracenyl, chrysenyl, fluorenyl, acenaphthacenyl, triphenylene orfluoranthene groups.

In the present disclosure, the heterocyclic group is a heterocyclicgroup containing at least one heteroatom selected from among O, N and S,and the number of carbon atoms thereof is preferably 2 to 60, but is notlimited thereto. Examples of the heterocyclic group include, but are notlimited to, thiophene, furan, pyrrol, imidazole, thiazole, oxazole,oxadiazole, triazole, pyridyl, bipyridyl, triazine, acridyl, pyridazine,quinolinyl, isoquinolinyl, indole, carbazole, benzoxazole,benzothiazole, benzimidazole, benzocarbazole, benzothiophene,dibenzothiophene, benzofuranyl, phenanthroline and dibenzofuranylgroups.

In the present disclosure, the imide group preferably contains 1 to 25carbon atoms, but is not limited thereto. Specific examples of the imidegroup include, but are not limited to, compounds having the followingformulas:

In the present disclosure, the amide group is an amide group whosenitrogen may be mono- or di-substituted with hydrogen, a straight,branched or cyclic chain alkyl group containing 1 to 25 carbon atoms oran aryl group containing 6 to 25 carbon atoms. Specific examples of theamide group include, but are not limited to, compounds having thefollowing formulas:

In the present disclosure, the ester group is an ester group whoseoxygen may be substituted with a straight, branched or cyclic chainalkyl group containing 1 to 25 carbon atoms or an aryl group containing6 to 25 carbon atoms. Specific examples of the ester group include, butare not limited to, compounds having the following formulas:

In the present disclosure, the heteroaryl group may be selected fromamong the above-described examples of the heterocyclic group.

In the present disclosure, the fluorenyl group has a structure in whichtwo cyclic organic compounds are linked to each other by one atom, andexamples thereof include

and the like.

In the present disclosure, the fluorenyl groups include an openfluorenyl group having a structure in which one of two cyclic compoundslinked to each other by one atom is broken.

Examples of the open fluorenyl group include

and the like.

In the present disclosure, the amine group preferably contains 1 to 30carbon atoms, but is not limited thereto. Specific examples of the aminegroup include, but are not limited to, methylamine, dimethylamine,ethylamine, diethylamine, phenylamine, naphthylamine, biphenylamine,anthracenylamine, 9-methyl-anthracenylamine, diphenylamine,phenylnaphthylamine, ditolylamine, phenyltolylamine and triphenylaminegroups.

In the present disclosure, examples of the arylamine group includesubstituted or unsubstituted monocyclic diarylamine, substituted orunsubstituted polycyclic diarylamine, and substituted or unsubstitutedmonocyclic or polycyclic diarylamine groups.

In the present disclosure, the aryl group of the aryloxy, arylthioxy,arylsulfoxy and aralkylamine groups is as defined above for the arylgroup.

In the present disclosure, the alkyl group of the alkylthioxy,alkylsulfoxy, alkylamine and aralkylamine groups is as defined above forthe alkyl group.

In the present disclosure, the heteroaryl group of the heteroarylaminegroup may be selected from among the above-described examples of theheterocyclic group.

In the present disclosure, the arylene, alkenylene, fluorenylene,carbazolylene and heteroarylene groups are divalent aryl, alkenyl,fluorenyl and carbazole groups, respectively. These groups are asdefined above for the aryl, alkenyl, fluorenyl and carbazole groups,except that they are divalent groups.

As used herein, the term “substituted or unsubstituted” means that it isunsubstituted or substituted with one or more selected from the groupconsisting of deuterium, a halogen group, an alkyl group, an alkenylgroup, an alkoxy group, a cycloalkyl group, a silyl group, anarylalkenyl group, an aryl group, an aryloxy group, an alkylthioxygroup, an alkylsulfoxy group, an arylsulfoxy group, a boron group, analkylamine group, an aralkylamine group, an arylamine group, aheteroaryl group, a carbazole group, an arylamine group, an aryl group,a fluorenyl group, a nitrile group, a nitro group, a hydroxyl group, anda heterocyclic group containing at least one heteroatom selected fromamong N, O and S.

In the present disclosure, the electron acceptor and the electron donormay be any conventional electron acceptor and electron donor known inthe field of organic solar cells. Specifically, the electron acceptor isa carbon-based aromatic compound or a heteroaromatic compound containingat least one heteroatom selected from among sulfur, phosphorus,nitrogen, selenium and the like.

In one embodiment of the present disclosure, the unit different from thefirst unit in the copolymer includes at least one of electron acceptorsrepresented by the following formulas:

whereinR₂ to R₅ are the same or different and are each independently selectedfrom the group consisting of hydrogen, deuterium, a halogen group, anitrile group, a nitro group, an imide group, an amide group, a hydroxylgroup, a substituted or unsubstituted alkyl group, a substituted orunsubstituted cycloalkyl group, a substituted or unsubstituted alkoxygroup, a substituted or unsubstituted aryloxy group, a substituted orunsubstituted alkylthioxy group, a substituted or unsubstitutedarylthioxy group, a substituted or unsubstituted alkylsulfoxy group, asubstituted or unsubstituted arylsulfoxy group, a substituted orunsubstituted alkenyl group, a substituted or unsubstituted silyl group,a substituted or unsubstituted boron group, a substituted orunsubstituted alkylamine group, a substituted or unsubstitutedaralkylamine group, a substituted or unsubstituted arylamine group, asubstituted or unsubstituted heteroarylamine group, a substituted orunsubstituted aryl group, a substituted or unsubstituted fluorenylgroup, a substituted or unsubstituted carbazole group, and a substitutedor unsubstituted heterocyclic group containing at least one heteroatomselected from among N, O and S, or adjacent two of R₂ to R₅ may form acondensed ring;X₁ and X₂ are the same or different and are each independently selectedfrom the group consisting of CRR′, NR, O, SiRR′, PR, S, GeRR′, Se andTe; andY₁ to Y₄ are the same or different and are each independently selectedfrom the group consisting of CR, N, SiR, P and GeR, wherein R and R′ arethe same or different and are each independently selected from the groupconsisting of hydrogen, deuterium, a halogen group, a nitrile group, anitro group, an imide group, an amide group, a hydroxyl group, asubstituted or unsubstituted alkyl group, a substituted or unsubstitutedcycloalkyl group, a substituted or unsubstituted alkoxy group, asubstituted or unsubstituted aryloxy group, a substituted orunsubstituted alkylthioxy group, a substituted or unsubstitutedarylthioxy group, a substituted or unsubstituted alkylsulfoxy group, asubstituted or unsubstituted arylsulfoxy group, a substituted orunsubstituted alkenyl group, a substituted or unsubstituted silyl group,a substituted or unsubstituted boron group, a substituted orunsubstituted alkylamine group, a substituted or unsubstitutedaralkylamine group, a substituted or unsubstituted arylamine group, asubstituted or unsubstituted heteroarylamine group, a substituted orunsubstituted aryl group, a substituted or unsubstituted fluorenylgroup, a substituted or unsubstituted carbazole group, and a substitutedor unsubstituted heterocyclic group containing at least one heteroatomselected from among N, O and S, or adjacent two of R and R′ may form acondensed ring.

In another embodiment of the present disclosure, the unit different fromthe first unit in the copolymer includes at least one of the electrondonors represented by the following formulas:

whereina is an integer ranging from 0 to 4;b is an integer ranging from 0 to 6;c is an integer ranging from 0 to 8;d and e are each an integer ranging from 0 to 3;R₂ and R₃ are the same or different and are each independently selectedfrom the group consisting of hydrogen, deuterium, a halogen group, anitrile group, a nitro group, an imide group, an amide group, a hydroxylgroup, a substituted or unsubstituted alkyl group, a substituted orunsubstituted cycloalkyl group, a substituted or unsubstituted alkoxygroup, a substituted or unsubstituted aryloxy group, a substituted orunsubstituted alkylthioxy group, a substituted or unsubstitutedarylthioxy group, a substituted or unsubstituted alkylsulfoxy group, asubstituted or unsubstituted arylsulfoxy group, a substituted orunsubstituted alkenyl group, a substituted or unsubstituted silyl group,a substituted or unsubstituted boron group, a substituted orunsubstituted alkylamine group, a substituted or unsubstitutedaralkylamine group, a substituted or unsubstituted arylamine group, asubstituted or unsubstituted heteroarylamine group, a substituted orunsubstituted aryl group, a substituted or unsubstituted fluorenylgroup, a substituted or unsubstituted carbazole group, and a substitutedor unsubstituted heterocyclic group containing at least one heteroatomselected from among N, O and S, or adjacent two of R₂ and R₃ may form acondensed ring;X₁ to X₃ are the same or different and are each independently selectedfrom the group consisting of CRR′, NR, O, SiRR′, PR, S, GeRR′, Se andTe;Y₁ and Y₂ are the same or different and are each independently selectedfrom the group consisting of CR, N, SiR, P and GeR; wherein R and R′ arethe same or different and are each independently selected from the groupconsisting of hydrogen, deuterium, a halogen group, a nitrile group, anitro group, an imide group, an amide group, a hydroxyl group, asubstituted or unsubstituted alkyl group, a substituted or unsubstitutedcycloalkyl group, a substituted or unsubstituted alkoxy group, asubstituted or unsubstituted aryloxy group, a substituted orunsubstituted alkylthioxy group, a substituted or unsubstitutedarylthioxy group, a substituted or unsubstituted alkylsulfoxy group, asubstituted or unsubstituted arylsulfoxy group, a substituted orunsubstituted alkenyl group, a substituted or unsubstituted silyl group,a substituted or unsubstituted boron group, a substituted orunsubstituted alkylamine group, a substituted or unsubstitutedaralkylamine group, a substituted or unsubstituted arylamine group, asubstituted or unsubstituted heteroarylamine group, a substituted orunsubstituted aryl group, a substituted or unsubstituted fluorenylgroup, a substituted or unsubstituted carbazole group, and a substitutedor unsubstituted heterocyclic group containing at least one heteroatomselected from among N, O and S, or adjacent two of R and R′ may form acondensed ring.

In one embodiment of the present disclosure, the copolymer comprises onerepresented by the following formula 2:

wherein l is a mole fraction in the range of 0<1≦l;m is a mole fraction in the range of 0≦m<1; l+m=1;n is an integer ranging from 1 to 10,000;A is represented by formula 1;B, C and D are the same or different and are each independently anelectron acceptor or an electron donor; andat least one of B, C and D is an electron acceptor.

In one embodiment of the present disclosure, B in formula 2 is anelectron acceptor.

In another embodiment, D in formula 2 is an electron acceptor.

In still another embodiment, B and D in formula 4 are each an electronacceptor.

In one embodiment of the present disclosure, the electron acceptor inthe copolymer is represented by the following formula 3:

whereins and t are each an integer ranging from 0 to 4; andR₈ to R₁₁ are the same or different and are each independently selectedfrom the group consisting of hydrogen, deuterium, a halogen group, anitrile group, a nitro group, an imide group, an amide group, a hydroxylgroup, a substituted or unsubstituted alkyl group, a substituted orunsubstituted cycloalkyl group, a substituted or unsubstituted alkoxygroup, a substituted or unsubstituted aryloxy group, a substituted orunsubstituted alkylthioxy group, a substituted or unsubstitutedarylthioxy group, a substituted or unsubstituted alkylsulfoxy group, asubstituted or unsubstituted arylsulfoxy group, a substituted orunsubstituted alkenyl group, a substituted or unsubstituted silyl group,a substituted or unsubstituted boron group, a substituted orunsubstituted alkylamine group, a substituted or unsubstitutedaralkylamine group, a substituted or unsubstituted arylamine group, asubstituted or unsubstituted heteroarylamine group, a substituted orunsubstituted aryl group, a substituted or unsubstituted fluorenylgroup, a substituted or unsubstituted carbazole group, and a substitutedor unsubstituted heterocyclic group containing at least one heteroatomselected from among N, O and S, or adjacent two of R₈ to R₁₁ may form acondensed ring.

In another embodiment of the present disclosure, the electron donor inthe copolymer is represented by the following formula 4:

whereinq and r are each an integer ranging from 0 to 3;R₆ and R₇ are the same or different and are each independently selectedfrom the group consisting of hydrogen, deuterium, a halogen group, anitrile group, a nitro group, an imide group, an amide group, a hydroxylgroup, a substituted or unsubstituted alkyl group, a substituted orunsubstituted cycloalkyl group, a substituted or unsubstituted alkoxygroup, a substituted or unsubstituted aryloxy group, a substituted orunsubstituted alkylthioxy group, a substituted or unsubstitutedarylthioxy group, a substituted or unsubstituted alkylsulfoxy group, asubstituted or unsubstituted arylsulfoxy group, a substituted orunsubstituted alkenyl group, a substituted or unsubstituted silyl group,a substituted or unsubstituted boron group, a substituted orunsubstituted alkylamine group, a substituted or unsubstitutedaralkylamine group, a substituted or unsubstituted arylamine group, asubstituted or unsubstituted heteroarylamine group, a substituted orunsubstituted aryl group, a substituted or unsubstituted fluorenylgroup, a substituted or unsubstituted carbazole group, and a substitutedor unsubstituted heterocyclic group containing at least one heteroatomselected from among N, O and S, or adjacent two of R₆ and R₇ may form acondensed ring; and R″ is selected from the group consisting ofhydrogen, deuterium, a halogen group, a nitrile group, a nitro group, animide group, an amide group, a hydroxyl group, a substituted orunsubstituted alkyl group, a substituted or unsubstituted cycloalkylgroup, a substituted or unsubstituted alkoxy group, a substituted orunsubstituted aryloxy group, a substituted or unsubstituted alkylthioxygroup, a substituted or unsubstituted arylthioxy group, a substituted orunsubstituted alkylsulfoxy group, a substituted or unsubstitutedarylsulfoxy group, a substituted or unsubstituted alkenyl group, asubstituted or unsubstituted silyl group, a substituted or unsubstitutedboron group, a substituted or unsubstituted alkylamine group, asubstituted or unsubstituted aralkylamine group, a substituted M orunsubstituted arylamine group, a substituted or unsubstitutedheteroarylamine group, a substituted or unsubstituted aryl group, asubstituted or unsubstituted fluorenyl group, a substituted orunsubstituted carbazole group, and a substituted or unsubstitutedheterocyclic group containing at least one heteroatom selected fromamong N, O and S.

The copolymer of the present disclosure comprises a 2,7-carbazole unitin addition to a 3,6-carbazole unit. This 2,7-carbazole unit provideslow band gap energy and is highly stable against chemical and thermalattacks, air and moisture compared to other electron donors, so that itimproves the efficiency of the organic solar cell comprising thecopolymer.

In one embodiment of the disclosure, the unit of formula 4 in thecopolymer is present in an amount of more than 0 mole % and 40 mole % orless based on the total moles of monomers constituting the copolymer.

In another embodiment, the present disclosure provides a copolymercomprising the first unit of formula 1, the second unit of formula 3 andthe third unit of formula 4.

In still another embodiment, the present disclosure provides a copolymercomprising the first unit of formula 1, the second unit of formula 3 andthe third unit of formula 4, wherein the first unit of formula 1 ispresent in an amount of greater than 0 mole % and 10 mole % or lessbased on the total moles of monomers constituting the copolymer, thesecond unit of formula 3 is present in an amount of greater than 0 mole% and 50 mole % or less based on the total moles of the monomers, andthe third unit of formula 4 is present in an amount of more than 0 mole% and 40 mole % or less based on the total moles of the monomers.

In still another embodiment, unit C of formula 2 is the electronacceptor of formula 3.

In still another embodiment, unit B of formula 2 is the electron donorof formula 4.

In still another embodiment, unit D of formula 2 is the electron donorof formula 4.

In still another embodiment, units B and C of formula 2 are eachrepresented by formula 4.

In one embodiment of the present disclosure, the copolymer isrepresented by the following formula 5:

wherein R₁, R_(a), R_(b), o and p are as defined in formula 1;q and r are each an integer ranging from 0 to 3;s and t are each an integer ranging from 0 to 4;l is a mole fraction in the range of 0<l≦1;m is a mole fraction in the range of 0≦m<1; l+m=1;n is an integer ranging from 1 to 10,000;R″ are the same or different and are each independently selected fromthe group consisting of hydrogen, deuterium, a halogen group, a nitrilegroup, a nitro group, an imide group, an amide group, a hydroxyl group,a substituted or unsubstituted alkyl group, a substituted orunsubstituted cycloalkyl group, a substituted or unsubstituted alkoxygroup, a substituted or unsubstituted aryloxy group, a substituted orunsubstituted alkylthioxy group, a substituted or unsubstitutedarylthioxy group, a substituted or unsubstituted alkylsulfoxy group, asubstituted or unsubstituted arylsulfoxy group, a substituted orunsubstituted alkenyl group, a substituted or unsubstituted silyl group,a substituted or unsubstituted boron group, a substituted orunsubstituted alkylamine group, a substituted or unsubstitutedaralkylamine group, a substituted or unsubstituted arylamine group, asubstituted or unsubstituted heteroarylamine group, a substituted orunsubstituted aryl group, a substituted or unsubstituted fluorenylgroup, a substituted or unsubstituted carbazole group, and a substitutedor unsubstituted heterocyclic group containing at least one heteroatomselected from among N, O and S; andR₆ to R₁₁ are the same or different and are each independently selectedfrom the group consisting of hydrogen, deuterium, a halogen group, anitrile group, a nitro group, an imide group, an amide group, a hydroxylgroup, a substituted or unsubstituted alkyl group, a substituted orunsubstituted cycloalkyl group, a substituted or unsubstituted alkoxygroup, a substituted or unsubstituted aryloxy group, a substituted orunsubstituted alkylthioxy group, a substituted or unsubstitutedarylthioxy group, a substituted or unsubstituted alkylsulfoxy group, asubstituted or unsubstituted arylsulfoxy group, a substituted orunsubstituted alkenyl group, a substituted or unsubstituted silyl group,a substituted or unsubstituted boron group, a substituted orunsubstituted alkylamine group, a substituted or unsubstitutedaralkylamine group, a substituted or unsubstituted arylamine group, asubstituted or unsubstituted heteroarylamine group, a substituted orunsubstituted aryl group, a substituted or unsubstituted fluorenylgroup, a substituted or unsubstituted carbazole group, and a substitutedor unsubstituted heterocyclic group containing at least one heteroatomselected from among N, O and S; or adjacent two of R₆ to R₁₁ may form acondensed ring.

In one embodiment of the present disclosure, R_(a) is hydrogen.

in another embodiment of the present disclosure, R_(b) is hydrogen.

In another embodiment of the present disclosure, s and t are each 1.

In still another embodiment of the present disclosure, R₈ is hydrogen.

In still another embodiment of the present disclosure, R₉ is hydrogen.

In still another embodiment of the present disclosure, is hydrogen.

In still another embodiment of the present disclosure, is hydrogen.

In still another embodiment of the present disclosure, is hydrogen.

In yet another embodiment of the present disclosure, R is hydrogen.

In one embodiment of the present invention, the copolymer furthercomprises a fourth unit represented by the following formula 6 and afifth unit represented by the following formula 7:

whereinl is a mole fraction in the range of 0<l≦1;m is a mole fraction in the range of 0≦m<1;l+m=1;R₁ is as defined in formula 1 above; andR″ is as defined in formula 4 above.

In one embodiment of the present disclosure, the end group of thecopolymer is selected from the group consisting of hydrogen, deuterium,a halogen group, a nitrile group, a nitro group, an imide group, anamide group, a hydroxyl group, a substituted or unsubstituted alkylgroup, a substituted or unsubstituted cycloalkyl group, a substituted orunsubstituted alkoxy group, a substituted or unsubstituted aryloxygroup, a substituted or unsubstituted alkylthioxy group, a substitutedor unsubstituted arylthioxy group, a substituted or unsubstitutedalkylsulfoxy group, a substituted or unsubstituted arylsulfoxy group, asubstituted or unsubstituted alkenyl group, a substituted orunsubstituted silyl group, a substituted or unsubstituted boron group, asubstituted or unsubstituted alkylamine group, a substituted orunsubstituted aralkylamine group, a substituted or unsubstitutedarylamine group, a substituted or unsubstituted heteroarylamine group, asubstituted or unsubstituted aryl group, a substituted or unsubstitutedfluorenyl group, a substituted or unsubstituted carbazole group, and asubstituted or unsubstituted heterocyclic group containing at least oneheteroatom selected from among N, O and S.

In one embodiment of the present disclosure, the end group of thecopolymer is a heterocyclic group.

In another embodiment of the present disclosure, the end group of thecopolymer is an aryl group.

In one embodiment of the present disclosure, the copolymer preferablyhas a number-average molecular weight of 500-1,000,000 g/mol, and morepreferably 10,000-100,000 g/mol.

In one embodiment of the present disclosure, the copolymer may have amolecular weight distribution of 1-100. Preferably, the copolymer has amolecular weight distribution of 1-3.

As the molecular weight distribution decreases and the number-averagemolecular weight increases, the electrical and mechanical properties ofthe copolymer improve.

In addition, in order for the copolymer to have a specific level orhigher of solubility so that a solution application method isadvantageously applied, the copolymer preferably has a number-averagemolecular weight of 100,000 or less.

The copolymer comprising the unit of formula 1 can be prepared based onPreparation Examples as described below.

The copolymer according to the present disclosure can be prepared by amulti-step chemical reaction. Specifically, monomers can be prepared byan alkylation reaction, the Grignard reaction, the Suzuki couplingreaction and the Stille coupling reaction, after final polymers can beprepared from the monomers by a carbon-carbon coupling reaction such asthe Stille coupling reaction. When the substituent to be introduced is aboronic acid or boronic ester compound, the copolymer can be prepared bythe Suzuki coupling reaction, and when the substituent to be introducedis a tributyltin compound, the copolymer can be prepared by the Stillecoupling reaction, but is not limited thereto.

In another aspect, the present disclosure provides an organic solar cellcomprising the copolymer containing the unit of formula 1.

Specifically, the present disclosure provides an organic solar cellcomprising: a first electrode; a second electrode opposite the firstelectrode; and one or more organic material layers interposed betweenthe first electrode and the second electrode and including a photoactivelayer, wherein one or more of the organic material layers comprise theabove-described copolymer.

In one embodiment of the present disclosure, the organic solar cellcomprises the first electrode, the photoactive layer and the secondelectrode. The organic solar cell may further comprise a substrate, ahole transport layer and/or an electron transport layer.

The substrate may be a glass or transparent substrate having excellenttransparency, surface smoothness, ease of handling, and waterresistance, but is not limited thereto.

The substrate is not limited as long as it is commonly used in organicsolar cells. Specific examples of the substrate include, but are notlimited to, polyethylene terephthalate (PET), polyethylene naphthalate(PEN), polypropylene (PP), polyimide (PI) and triacetyl cellulose (TAC).

The first electrode may be made of a transparent, highly conductivematerial, but is not limited thereto. Specific examples of the materialof the first electrode include, but are not limited to, indium tin oxide(ITO), tin oxide (SnO₂) and zinc oxide (ZnO).

The second electrode may be made of a metal having a low work function,but is not limited thereto. Specific examples of the material of thesecond electrode include, but are not limited to, metals, such aslithium, magnesium or aluminum, alloys thereof, and multilayermaterials, such as Al:Li, Al:BaF₂, or Al:BaF₂:Ba.

The hole transport layer and/or the electron transport layer may be madeof a material which efficiently transfers electrons and holes to thephotoactive layer to increase the mobility of produced charges to theelectrodes, but is not limited thereto.

Examples of the material of the hole transport layer induce PEDOT:PSS(poly(3,4-ethylenediocythiophene) doped with poly(styrenesulfonicacid)), andN,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine(TPD). Examples of the material of the electron transport layer includealuminum trihydroxyquinoline (Alq₃), the 1,3,4-oxadiazole derivative PBD(2-(4-bipheyl)-5-phenyl-1,3,4-oxadiazole), the quinoxaline derivativeTPQ (1,3,4-tris[(3-phenyl-6-trifluoromethyl)qunoxaline-2-yl]benzene),and triazole derivatives.

The photoactive layer may comprise an electron donor material and anelectron acceptor material.

In one embodiment of the present disclosure, the electron donor materialis the copolymer comprising the first unit of formula 1.

In one embodiment of the present disclosure, the electron acceptormaterial may be selected from the group consisting of fullerene,fullerene derivatives, vasocuproin, semiconductor elements,semiconductor compounds, or combinations thereof. Specifically, theelectron acceptor material may be phenyl C₆₁-butyric acid methyl ester(PC₆₁BM) or phenyl C₇₁-butyric acid methyl ester (PC₇₁BM).

The electron donor material and the electron acceptor material in thephotoactive layer can form a bulk heterojunction (BHJ). The electrondonor material and the electron acceptor material may be mixed with eachother at a ratio of 1:10-10:1 (w/w). After the electron donor materialand the electron acceptor material have been mixed, they may be annealedat a temperature of 30 to 300° C. for 1 second to 24 hours in order tomaximize the characteristics thereof.

The thickness of the photoactive layer may be 10-10,000 Å, but is notlimited thereto.

In one embodiment of the present disclosure, a buffer layer may furtherbe introduced between the photoactive layer and the first electrode, andan electron transfer layer, a hole blocking layer or an optical spacelayer may further be introduced between the photoactive layer and thesecond electrode.

As described in Korean Patent Laid-Open Publication No. 10-2010-0111767which is incorporated herein by reference, in one preferred embodiment,the organic solar cell comprises the substrate, the first electrode, thephotoactive layer and the second electrode. Herein, the photoactivelayer comprises an electrode donor made of the copolymer, whichcomprises the first unit of formula 1, and an electron acceptor made ofa C60 fullerene derivative or a C70 fullerene derivative.

In one embodiment of the present disclosure, the photovoltaic materialof the photoactive layer comprises the copolymer comprising the firstunit of formula 1, and the electron acceptor, which are mixed with eachother at a weight ratio of 1:0.5-1:4.

In another embodiment of the present disclosure, the photovoltaicmaterial of the photoactive layer comprises the copolymer comprising thefirst unit of formula 1, and a C60 fullerene derivative or a C70fullerene derivative, which are mixed with each other at a weight ratioof 1:0.5-1:4.

If the fullerene derivative is used at a weight ratio of less than 0.5relative to the copolymer comprising the first unit of formula 1, themobility of electrons will be insufficient, because the content of thecrystallized fullerene derivative will be insufficient, and if thefullerene derivative is used at a weight ratio of more than 4, theefficient absorption of light into the photoactive layer will not beachieved, because the amount of the copolymer comprising the first unitof formula 1 is relatively reduced.

In one embodiment of the present disclosure, the organic solar cell mayeither comprise an anode, a photoactive electrode and a cathode, whichare arranged in that order, or comprise a cathode, a photoactive layerand an anode, which are arranged in that order, but the scope of thepresent invention is not limited thereto.

In another embodiment of the present disclosure, the organic solar cellmay either comprise an anode, a hole transport layer, a photoactivelayer, an electron transport layer and a cathode, which are arranged inthat order, or comprise a cathode, an electron transport layer, aphotoactive layer, a hole transport layer and an anode, which arearranged in that order, but the scope of the present invention is notlimited thereto.

The organic solar cell of the present disclosure can be fabricated usingthe same materials and method as known in the art, except that theorganic material layers comprise the copolymer comprising the first unitof formula which is the compound of the present disclosure.

In another aspect, the present disclosure provides a method forfabricating an organic solar cell, the method comprising the steps of:preparing a substrate; forming a first electrode on a region of rearsides of the substrate; forming on the first layer an organic materiallayer comprising the copolymer including the first unit of formula 1;and forming a second electrode on the organic material layer.

The organic solar cell of the present invention can be fabricated, forexample, by sequentially depositing the first electrode, the organicmaterial layer and the second electrode on the substrate. Herein, thedeposition can be performed using wet coating methods, including gravureprinting, offset printing, screen printing, inkjet printing, spincoating, and spray coating, but is not limited thereto.

In the organic solar cell comprising the copolymer including the firstunit of formula 1, the copolymer can serve as an electron donor.

Hereinafter, a method for preparing the first unit of formula 1, and amethod for fabricating an organic solar cell using these units will bedescribed in detail with reference to examples. It is to be understood,however, that these examples are for illustrative purposes only and arenot intended to limit the scope of the present invention.

Example 1 Synthesis of Monomers Example 1-A Preparation ofN-9′-heptadecanyl-3,6-dibromocarbazole

In this Example, 9-heptadecane p-toluenesulfonate was prepared withreference to the literature (B. Nicolas, M. Alexandre, M. Leclerc, Adv.Mater. 19, 2295-2300).

3,6-Dibromo-9H-carbazole (4.00 g, 12.3 mmol) and potassium hydroxide(6.90 q, 123 mmol) were added to 30 ml of anhydrous dimethyl sulfoxideand stirred for 1 hour. Then, 9-heptadecane p-toluenesulfonate (7.58 g,18.5 mmol) was added thereto and stirred for 12 hours.

The mixture was cooled to room temperature, extracted with hexane/ethylacetate (3:1 v/v) and washed with water, after which the solution wasdried with magnesium sulfate (MgSO₄) to remove water. The solvent wasremoved under reduced pressure, and the residue was purified by silicagel column chromatography to afford a white solid.

Yield: 86%

¹H NMR: (300 MHz, CDCl3, ppm): δ 8.16 (br, 2H); 7.48 (br, 4H); 4.47 (br,1H); 2.23 (br, 2H); 1.90 (br, 2H); 1.11 (br, 24H); 0.83 (t, J=7.1 Hz,6H)

¹³C NMR (75 MHz, CDCl₃, ppm): δ 129.39; 128.93; 123.73; 123.40; 113.42;110.94; 57.23; 34.03; 32.13; 29.68; 29.66; 29.50; 27.02; 22.99; 14.47

m.p.: 53.6 to 55.7° C.

HRMS (EI⁺, m/z) [M]⁺ calculated for C₂₉H₄₁Br₂N: 561.1606. found:561.1608.

Example 1-B Preparation of3,6-bis(4′,4′,5′,5′-tetramethyl-1′,3′,2′-dioxaborolan-2′-yl)-N-9′-heptadecanylcarbazole

N-9′-Heptadecanyl-3,6-dibromocarbazole (4.00 q, 7.10 mmol) was added toand dissolved in 30 ml of anhydrous tetrahydrofuran) and cooled to −78°C., and 1.7 M n-butyllithium in hexane (17.5 ml, 29.8 mmol) was addedthereto. The mixture was stirred for 1 hour, and then2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (5.28 g, 28.4 mmol)was added at a time thereto. Then, the mixture was warmed to roomtemperature and stirred for 12 hours.

Water was added to the mixture to stop the reaction, and the mixture wasextracted with diethyl ether and washed with water, after which thesolution was dried with magnesium sulfate (MgSO₄) to remove water. Thesolvent was removed under reduced pressure, and the residue was purifiedby silica gel column chromatography to afford a white solid.

Yield: 57%

¹H NMR (300 MHz, CDCl₃, ppm): δ 8.68 (br, 2H); 7.87 (br, 2H); 7.56 (br,1H); 7.39 (br, 1H); 4.58 (br, 1H); 2.29 (br, 2H); 1.90 (br, 2H); 1.39(br, 24H); 1.13 (br, 24H); 0.81 (t, J=6.8 Hz, 6H)

¹³C NMR (75 MHz, CDCl₃, ppm): δ 144.61; 141.20; 132.08; 128.40; 124.25;122.85; 111.39; 108.66; 83.90; 56.94; 34.10; 32.14; 29.68; 27.10; 25.36;22.99; 14.47

m.p.: 147.8˜149.2° C.

HRMS (EI⁺, m/z) [M]⁺ calculated for C₂₉H₄₁Br₂N: 567.5100. found:567.5103

In this Example,2,7-bis(4′,4′,5′,5′-tetramethyl-1′,3′,2′-dioxaborolan-2′-yl)-N-9′-heptadecanylcarbazolewas prepared with reference to the literature (B. Nicolas, M. Alexandre,M. Leclerc, Adv. Mater. 19, 2295-2300).

Example 2 Synthesis of Copolymer 1

3,6-Bis(4′,4′,5′,5′-tetramethyl-1′,3′,2′-dioxaborolan-2′-yl)-N-9′-heptadecanylcarbazole(4.1 mg, 0.006 mmol),2,7-Bis(4′,4′,5′,5′-tetramethyl-1′,3′,2′-dioxaborolan-2′-yl)-N-9′-heptadecanylcarbazole(201 mg, 0.306 mmol), 4,7-bis-(5-bromo-2-thienyl)-2,1,3-benzothiadiazole(143 mg, 0.312 mmol), a 20% aqueous solution of tetraethylammoniumhydroxide (3 ml), tetrakis(triphenylphosphine)palladium (0) (5 mg) andAliquat 336 were added to 3 ml of toluene and stirred under reflux.After 72 hours, phenylboronic acid (0.05 g) was added to and reactedwith the reaction mixture for 3 hours, after which bromobenzene (0.12 g)was added to and reacted with the mixture for 4 hours. Then, the mixturewas cooled to room temperature and poured into methanol. The solid wasfiltered and Soxhlet-extracted with acetone, hexane and chloroform. Theextract was precipitated in methanol, and the solid was filtered.

Yield: 55%

Number-average molecular weight: 9,400 g/mol

Weight-average molecular weight: 33,300 g/mol

Example 3 Synthesis of Copolymer 2

3,6-Bis(4′,4′,5′5′-tetramethyl-1′,3′,2′-dioxaborolan-2′-yl)-N-9′-heptadecanylcarbazole(20.5 mg, 0.030 mmol),2,7-Bis(4′,4′,5′,5′-tetramethyl-1′,3′,2′-dioxaborolan-2′-yl)-N-9′-heptadecanylcarbazole(184 mg, 0.281 mmol), 4,7-bis-(5-bromo-2-thienyl)-2,1,3-benzothiadiazole(143 mg, 0.312 mmol), a 20% aqueous solution of tetraethylammoniumhydroxide (3 ml), tetrakis(triphenylphosphine)palladium (0) (5 mg) andAliquat 336 were added to 3 ml of toluene and stirred under reflux.After 72 hours, phenylboronic acid (0.05 g) was added to and reactedwith the reaction mixture for 3 hours, after which bromobenzene (0.12 g)was added to and reacted with the mixture for 4 hours. Then, the mixturewas cooled to room temperature and poured into methanol. The solid wasfiltered and Soxhlet-extracted with acetone, hexane and chloroform. Theextract was precipitated in methanol, and the solid was filtered.

Yield: 58%

Number-average molecular weight: 11,100 g/mol

Weight-average molecular weight: 56,400 g/mol

Example 4 Synthesis of Copolymer 3

3,6-Bis(4′,4′,5′,5′-tetramethyl-1′,3′,2′-dioxaborolan-2,7-yl)—N-9′-heptadecanylcarbazole(41.0 mg, 0.062 mmol), 2,7-heptadecanylcarbazole (164 mg, 0.250 mmol),4,7-bis-(5-bromo-2-thienyl)-2,1,3-benzothiadiazole (143 mg, 0.312 mmol),a 20% aqueous solution of tetraethylammonium hydroxide (3 ml),tetrakis(triphenylphosphine)palladium (0) (5 mg) and Aliquat 336 wereadded to 3 ml of toluene and stirred under reflux. After 72 hours,phenylboronic acid (0.05 g) was added to and reacted with the reactionmixture for 3 hours, after which bromobenzene (0.12 g) was added to andreacted with the mixture for 4 hours. Then, the mixture was cooled toroom temperature and poured into methanol. The solid was filtered andSoxhlet-extracted with acetone, hexane and chloroform extract wasprecipitated in methanol, and the solid was filtered.

Yield: 60%

Number-average molecular weight: 10,700 g/mol

Weight-average molecular weight: 20,500 g/mol

Comparative Example 1 Synthesis of Copolymer 4

2,7-Bis(4′,4′,5′,5′-tetramethyl-1′,3′,2′-dioxaborolan-2′-yl)—N-9′-heptadecanylcarbazole(205 mg, 0.312 mmol), 4,7-bis-(5-bromo-2-thienyl)-2,1,3-benzothiadiazole(143 mg, 0.312 mmol), a 20% aqueous solution of tetraethylammoniumhydroxide, tetrakis(triphenylphosphine)palladium (0) (5 mg) and Aliquat336 were added to 3 ml of toluene and stirred under reflux. After 72hours, phenylboronic acid (0.05 g) was added to and reacted with thereaction mixture for 3 hours, after which bromobenzene (0.12 g) wasadded to and reacted with the mixture for 4 hours. Then, the mixture wascooled to room temperature and poured into methanol. The solid wasfiltered and Soxhlet-extracted with acetone, hexane and chloroform. Theextract was precipitated in methanol, and the solid was filtered.

Comparative Example 2 Synthesis of Copolymer 5

3,6-Bis(4′,4′,5′,5′-tetramethyl-1′,3′,2′-dioxaborolan-2′-yl)-N-9′-heptadecanylcarbazole(200 mg, 0.304 mmol), 4,7-bis-(5-bromo-2-thienyl)-2,1,3-benzothiadiazole(139 mg, 0.304 mmol), a 20% aqueous solution of tetraethylammoniumhydroxide (3 ml), tetrakis(triphenylphosphine)palladium (0) (5 mg) andAliquat 336 were added to 3 ml of toluene and stirred under reflux.After 72 hours, phenylboronic acid (0.05 g) was added to and reactedwith the reaction mixture for 3 hours, after which bromobenzene (0.12 g)was added to and reacted with the mixture for 4 hours. Then, the mixturewas cooled to room temperature and poured into methanol. The solid wasfiltered and Soxhlet-extracted with acetone, hexane and chloroform. Theextract was precipitated in methanol, and the solid was filtered.

Yield: 42%

Number-average molecular weight: 4,500 g/mol

Weight-average molecular weight: 6,100 g/mol

Fabricate of Organic Solar Cells and Measurement of Properties Thereof

Each of the above-prepared copolymers and PC₇₁BM (|6,6|-phenyl C₆₁butyric acid methyl ester were dissolved in 1,2-dichlorobenzene (DCB) toprepare composite solutions. Herein, the concentration of the copolymerin the composite solution was adjusted to 1-2 wt %. In order tofabricate organic solar cells having a structure ofITO/PEDOT:PSS/photoactive layer/LiF/Al, a glass substrate coated withITO was ultrasonically washed with distilled water, acetone and2-propanol, and the surface of the ITO was treated with ozone for 10minutes, and then spin-coated with PEDOT:PSS (AI 4083) to a thickness of25 nm, followed by heat treatment at 235° C. for 10 minutes. For coatingof the photoactive layer, each of the polymer-PC₇₁BM composite solutionswas filtered with a 0.45-μm PP syringe filter and spin-coated on thePEDOT:PSS layer, followed by heat treatment at 120° C. for 5 minutes.Then, LiF was deposited on the photoactive layer to a thickness of 6 Åunder a vacuum of 3×10⁻⁸ torr using a thermal evaporator, after which Alwas deposited on the LiF to a thickness of 120 nm. The photovoltaicproperties of the organic solar cells fabricated as described above weremeasured under a condition of 100 mW/cm² (AM 1.5), and the results ofthe measurement are shown in Table 1 below.

TABLE 1 Properties of organic solar cells short circuit open circuitpower conversion Molar ratio (%) current density voltage Fill efficiencyCopolymer of 3,6-carbazole (mA/cm2) (V) factor (%) Example 2 Copolymer 11 13.6 0.91 50 6.2 Example 3 Copolymer 2 5 10.5 0.91 50.9 4.9 Example 4Copolymer 3 10 10.9 0.92 41.3 4.2 Comparative Copolymer 4 0 12.6 0.9139.6 4.6 Example 1 Comparative Copolymer 5 100 1.8 0.50 23.6 0.2 Example2

FIG. 2 is a graphic diagram showing current-voltage curves for theorganic solar cells.

As can be seen from the results in Table 1 above, the organic solarcells of Examples 2 to 4, which comprise the copolymer including thefirst unit of formula 1, had increased efficiency compared to theorganic solar cell of Comparative Example 1, comprising the copolymerwhich does not include the first unit of formula 1, and the organicsolar cell of Comparative Example 2, which comprises the copolymerincluding only the first unit of formula 1.

As can be seen from the results in Table 1, the short-circuit density,fill factor and energy conversion efficiency of the organic solar cellswere influenced by the molar ratio of the first unit of formula 1.

Accordingly, it can be concluded that the mobility of holes in thephotoactive layer of the organic solar cell is increased due to thepresence of 3,6-carbazole so as to approach the mobility of electrons,thereby increasing the energy conversion efficiency of the organic solarcell.

As described above, the copolymer of the present disclosure can be usedas a material for the organic material layer of an organic solar cell,and an organic solar cell comprising the same can exhibit excellentproperties, including increased open voltage and increased efficiency.In particular, the novel copolymer according to the present disclosurehas a deep HOMO level and high charge mobility, and thus can exhibitexcellent properties. Furthermore, the copolymer according to thepresent invention may be used in a pure or impure form in an organicsolar cell and may be applied using a solution application method. Inaddition, the copolymer of the present disclosure can increase theoptical efficiency of the organic solar cell and improve the cycle lifecharacteristics of the organic solar cell thanks to its thermalstability.

1. A copolymer comprising a first unit represented by the followingformula 1 and at least one unit different from the first unit, whereinthe first unit is present in an amount of greater than 0 mole % and 45mole % or less based on the total moles of monomers constituting thecopolymer:

wherein and p are each an integer ranging from 0 to 3; R_(a) and R_(b)are the same or different and are each independently selected from thegroup consisting of hydrogen, deuterium, a halogen group, a nitrilegroup, a nitro group, an imide group, an amide group, a hydroxyl group,a substituted or unsubstituted alkyl group, a substituted orunsubstituted cycloalkyl group, a substituted or unsubstituted alkoxygroup, a substituted or unsubstituted aryloxy group, a substituted orunsubstituted alkylthioxy group, a substituted or unsubstitutedarylthioxy group, a substituted or unsubstituted alkylsulfoxy group, asubstituted or unsubstituted arylsulfoxy group, a substituted orunsubstituted alkenyl group, a substituted or unsubstituted silyl group,a substituted or unsubstituted boron group, a substituted orunsubstituted alkylamine group, a substituted or unsubstitutedaralkylamine group, a substituted or unsubstituted arylamine group, asubstituted or unsubstituted heteroarylamine group, a substituted orunsubstituted aryl group, a substituted or unsubstituted fluorenylgroup, a substituted or unsubstituted carbazole group, and a substitutedor unsubstituted heterocyclic group containing at least one heteroatomselected from among N, O and S, or adjacent two of R_(a) and R_(b) mayform a condensed ring; and R₁ is selected from the group consisting ofhydrogen, deuterium, a halogen group, a nitrile group, a nitro group, animide group, an amide group, a hydroxyl group, a substituted orunsubstituted alkyl group, a substituted or unsubstituted cycloalkylgroup, a substituted or unsubstituted alkoxy group, a substituted orunsubstituted aryloxy group, a substituted or unsubstituted alkylthioxygroup, a substituted or unsubstituted arylthioxy group, a substituted orunsubstituted alkylsulfoxy group, a substituted or unsubstitutedarylsulfoxy group, a substituted or unsubstituted alkenyl group, asubstituted or unsubstituted silyl group, a substituted or unsubstitutedboron group, a substituted or unsubstituted alkylamine group, asubstituted or unsubstituted aralkylamine group, a substituted orunsubstituted arylamine group, a substituted or unsubstitutedheteroarylamine group, a substituted or unsubstituted aryl group, asubstituted or unsubstituted fluorenyl group, a substituted orunsubstituted carbazole group, and a substituted or unsubstitutedheterocyclic group containing at least one heteroatom selected fromamong N, O and S.
 2. The copolymer of claim 1, wherein the unitdifferent from the first unit includes at least one electron acceptor.3. The copolymer of claim 2, wherein the electron acceptor is present inan amount of greater than 0 mole % and 50 mole % or less based on thetotal moles of the monomers.
 4. The copolymer of claim 1, wherein theunit different from the first unit includes at least one electronacceptor and at least one electron donor.
 5. The copolymer of claim 1,wherein the unit different from the first unit includes at least twoelectron acceptors and at least one electron donor.
 6. The copolymer ofclaim 1, wherein the unit different from the first unit includes atleast one of electron acceptors represented by the following formulas:

wherein R₂ to R₅ are the same or different and are each independentlyselected from the group consisting of hydrogen, deuterium, a halogengroup, a nitrile group, a nitro group, an imide group, an amide group, ahydroxyl group, a substituted or unsubstituted alkyl group, asubstituted or unsubstituted cycloalkyl group, a substituted orunsubstituted alkoxy group, a substituted or unsubstituted aryloxygroup, a substituted or unsubstituted alkylthioxy group, a substitutedor unsubstituted arylthioxy group, a substituted or unsubstitutedalkylsulfoxy group, a substituted or unsubstituted arylsulfoxy group, asubstituted or unsubstituted alkenyl group, a substituted orunsubstituted silyl group, a substituted or unsubstituted boron group, asubstituted or unsubstituted alkylamine group, a substituted orunsubstituted aralkylamine group, a substituted or unsubstitutedarylamine group, a substituted or unsubstituted heteroarylamine group, asubstituted or unsubstituted aryl group, a substituted or unsubstitutedfluorenyl group, a substituted or unsubstituted carbazole group, and asubstituted or unsubstituted heterocyclic group containing at least oneheteroatom selected from among N, O and S, or adjacent two of R₂ to R₅may form a condensed ring; X₁ to X₃ are the same or different and areeach independently selected from the group consisting of CRR′, NR, O,SiRR′, PR, S, GeRR′, Se and Te; and Y₁ to Y₄ are the same or differentand are each independently selected from the group consisting of CR, N,SiR, P and GeR; wherein R and R′ are the same or different and are eachindependently selected from the group consisting of hydrogen, deuterium,a halogen group, a nitrile group, a nitro group, an imide group, anamide group, a hydroxyl group, a substituted or unsubstituted alkylgroup, a substituted or unsubstituted cycloalkyl group, a substituted orunsubstituted alkoxy group, a substituted or unsubstituted aryloxygroup, a substituted or unsubstituted alkylthioxy group, a substitutedor unsubstituted arylthioxy group, a substituted or unsubstitutedalkylsulfoxy group, a substituted or unsubstituted arylsulfoxy group, asubstituted or unsubstituted alkenyl group, a substituted orunsubstituted silyl group, a substituted or unsubstituted boron group, asubstituted or unsubstituted alkylamine group, a substituted orunsubstituted aralkylamine group, a substituted or unsubstitutedarylamine group, a substituted or unsubstituted heteroarylamine group, asubstituted or unsubstituted aryl group, a substituted or unsubstitutedfluorenyl group, a substituted or unsubstituted carbazole group, and asubstituted or unsubstituted heterocyclic group containing at least oneheteroatom selected from among N, O and S, or adjacent two of R and R′may form a condensed ring.
 7. The copolymer of claim 1, wherein the unitdifferent from the first unit includes at least one of electron donorsrepresented by the following formulas:

wherein a is an integer ranging from 0 to 4; b is an integer rangingfrom 0 to 6; c is an integer ranging from 0 to 8; d and e are each aninteger ranging from 0 to 3; R₂ and R₃ are the same or different and areeach independently selected from the group consisting of hydrogen,deuterium, a halogen group, a nitrile group, a nitro group, an imidegroup, an amide group, a hydroxyl group, a substituted or unsubstitutedalkyl group, a substituted or unsubstituted cycloalkyl group, asubstituted or unsubstituted alkoxy group, a substituted orunsubstituted aryloxy group, a substituted or unsubstituted alkylthioxygroup, a substituted or unsubstituted arylthioxy group, a substituted orunsubstituted alkylsulfoxy group, a substituted or unsubstitutedarylsulfoxy group, a substituted or unsubstituted alkenyl group, asubstituted or unsubstituted silyl group, a substituted or unsubstitutedboron group, a substituted or unsubstituted alkylamine group, asubstituted or unsubstituted aralkylamine group, a substituted orunsubstituted arylamine group, a substituted or unsubstitutedheteroarylamine group, a substituted or unsubstituted aryl group, asubstituted or unsubstituted fluorenyl group, a substituted orunsubstituted carbazole group, and a substituted or unsubstitutedheterocyclic group containing at least one heteroatom selected fromamong N, O and S, or adjacent two of R₂ and R₃ may form a condensedring; X₁ to X₃ are the same or different and are each independentlyselected from the group consisting of CRR′, NR, O, SiRR′, PR, S, GeRR′,Se and Te; and Y₁ and Y₂ are the same or different and are eachindependently selected from the group consisting of CR, N, SiR, P andGeR, wherein R and R′ are the same or different and are eachindependently selected from the group consisting of hydrogen, deuterium,a halogen group, a nitrile group, a nitro group, an imide group, anamide group, a hydroxyl group, a substituted or unsubstituted alkylgroup, a substituted or unsubstituted cycloalkyl group, a substituted orunsubstituted alkoxy group, a substituted or unsubstituted aryloxygroup, a substituted or unsubstituted alkylthioxy group, a substitutedor unsubstituted arylthioxy group, a substituted or unsubstitutedalkylsulfoxy group, a substituted or unsubstituted arylsulfoxy group, asubstituted or unsubstituted alkenyl group, a substituted orunsubstituted silyl group, a substituted or unsubstituted boron group, asubstituted or unsubstituted alkylamine group, a substituted orunsubstituted aralkylamine group, a substituted or unsubstitutedarylamine group, a substituted or unsubstituted heteroarylamine group, asubstituted or unsubstituted aryl group, a substituted or unsubstitutedfluorenyl group, a substituted or unsubstituted carbazole group, and asubstituted or unsubstituted heterocyclic group containing at least oneheteroatom selected from among N, O and S.
 8. The copolymer of claim 1,wherein the copolymer comprises one represented by the following formula2:

wherein l is a mole fraction in the range of 0<l≦1; m is a mole fractionin the range of 0≦m<1; l+m=1; n is an integer ranging from 1 to 10,000;A is represented by formula 1; B, C and D are the same or different andare each independently an electron acceptor or an electron donor; and atleast one of B, C and D is an electron acceptor.
 9. The copolymer ofclaim 2, wherein the electron acceptor is represented by the followingformula 3:

wherein s and t are each an integer ranging from 0 to 4; R₈ to R₁₁ arethe same or different and are each independently selected from the groupconsisting of hydrogen, deuterium, a halogen group, a nitrile group, anitro group, an imide group, an amide group, a hydroxyl group, asubstituted or unsubstituted alkyl group, a substituted or unsubstitutedcycloalkyl group, a substituted or unsubstituted alkoxy group, asubstituted or unsubstituted aryloxy group, a substituted orunsubstituted alkylthioxy group, a substituted or unsubstitutedarylthioxy group, a substituted or unsubstituted alkylsulfoxy group, asubstituted or unsubstituted arylsulfoxy group, a substituted orunsubstituted alkenyl group, a substituted or unsubstituted silyl group,a substituted or unsubstituted boron group, a substituted orunsubstituted alkylamine group, a substituted or unsubstitutedaralkylamine group, a substituted or unsubstituted arylamine group, asubstituted or unsubstituted heteroarylamine group, a substituted orunsubstituted aryl group, a substituted or unsubstituted fluorenylgroup, a substituted or unsubstituted carbazole group, and a substitutedor unsubstituted heterocyclic group containing at least one heteroatomselected from among N, O and S, or adjacent two of R₈ to R₁₁ may form acondensed ring.
 10. The copolymer of claim 4, wherein the electronacceptor is represented by the following formula:

wherein s and t are each an integer ranging from 0 to 4; and R₈ to R₁₁are the same or different and are each independently selected from thegroup consisting of hydrogen, deuterium, a halogen group, a nitrilegroup, a nitro group, an imide group, an amide group, a hydroxyl group,a substituted or unsubstituted alkyl group, a substituted orunsubstituted cycloalkyl group, a substituted or unsubstituted alkoxygroup, a substituted or unsubstituted aryloxy group, a substituted orunsubstituted alkylthioxy group, a substituted or unsubstitutedarylthioxy group, a substituted or unsubstituted alkylsulfoxy group, asubstituted or unsubstituted arylsulfoxy group, a substituted orunsubstituted alkenyl group, a substituted or unsubstituted silyl group,a substituted or unsubstituted boron group, a substituted orunsubstituted alkylamine group, a substituted or unsubstitutedaralkylamine group, a substituted or unsubstituted arylamine group, asubstituted or unsubstituted heteroarylamine group, a substituted orunsubstituted aryl group, a substituted or unsubstituted fluorenylgroup, a substituted or unsubstituted carbazole group, and a substitutedor unsubstituted heterocyclic group containing at least one heteroatomselected from among N, O and S, or adjacent two of R₈ to R₁₁ may form acondensed ring.
 11. The copolymer of claim 4, wherein the electron donoris represented by the following formula 4:

wherein q and r are each an integer ranging from 0 to 3; R₆ and R₇ arethe same or different and are each independently selected from the groupconsisting of hydrogen, deuterium, a halogen group, a nitrile group, anitro group, an imide group, an amide group, a hydroxyl group, asubstituted or unsubstituted alkyl group, a substituted or unsubstitutedcycloalkyl group, a substituted or unsubstituted alkoxy group, asubstituted or unsubstituted aryloxy group, a substituted orunsubstituted alkylthioxy group, a substituted or unsubstitutedarylthioxy group, a substituted or unsubstituted alkylsulfoxy group, asubstituted or unsubstituted arylsulfoxy group, a substituted orunsubstituted alkenyl group, a substituted or unsubstituted silyl group,a substituted or unsubstituted boron group, a substituted orunsubstituted alkylamine group, a substituted or unsubstitutedaralkylamine group, a substituted or unsubstituted arylamine group, asubstituted or unsubstituted heteroarylamine group, a substituted orunsubstituted aryl group, a substituted or unsubstituted fluorenylgroup, a substituted or unsubstituted carbazole group, and a substitutedor unsubstituted heterocyclic group containing at least one heteroatomselected from among N, O and S, or adjacent two of R₆ and R₇ may form acondensed ring; and R″ is selected from the group consisting ofhydrogen, deuterium, a halogen group, a nitrile group, a nitro group, animide group, an amide group, a hydroxyl group, a substituted orunsubstituted alkyl group, a substituted or unsubstituted cycloalkylgroup, a substituted or unsubstituted alkoxy group, a substituted orunsubstituted aryloxy group, a substituted or unsubstituted alkylthioxygroup, a substituted or unsubstituted arylthioxy group, a substituted orunsubstituted alkylsulfoxy group, a substituted or unsubstitutedarylsulfoxy group, a substituted or unsubstituted alkenyl group, asubstituted or unsubstituted silyl group, a substituted or unsubstitutedboron group, a substituted or unsubstituted alkylamine group, asubstituted or unsubstituted aralkylamine group, a substituted orunsubstituted arylamine group, a substituted or unsubstitutedheteroarylamine group, a substituted or unsubstituted aryl group, asubstituted or unsubstituted fluorenyl group, a substituted orunsubstituted carbazole group, and a substituted or unsubstitutedheterocyclic group containing at least one heteroatom selected fromamong N, O and S.
 12. A copolymer comprising a first unit represented bythe following formula 1, a second unit represented by the followingformula 3 and a third unit represented by the following formula 4:

wherein o, p, q and r are each an integer ranging from 0 to 3; S and tare each an integer ranging from 0 to 4; R₁ and R″ are the same ordifferent and are each independently selected from the group consistingof hydrogen, deuterium, a halogen group, a nitrile group, a nitro group,an imide group, an amide group, a hydroxyl group, a substituted orunsubstituted alkyl group, a substituted or unsubstituted cycloalkylgroup, a substituted or unsubstituted alkoxy group, a substituted orunsubstituted aryloxy group, a substituted or unsubstituted alkylthioxygroup, a substituted or unsubstituted arylthioxy group, a substituted orunsubstituted alkylsulfoxy group, a substituted or unsubstitutedarylsulfoxy group, a substituted or unsubstituted alkenyl group, asubstituted or unsubstituted silyl group, a substituted or unsubstitutedboron group, a substituted or unsubstituted alkylamine group, asubstituted or unsubstituted aralkylamine group, a substituted orunsubstituted arylamine group, a substituted or unsubstitutedheteroarylamine group, a substituted or unsubstituted aryl group, asubstituted or unsubstituted fluorenyl group, a substituted orunsubstituted carbazole group, and a substituted or unsubstitutedheterocyclic group containing at least one heteroatom selected fromamong N, O and S; and R_(a), R_(b) and R₆ to R₁₁ are the same ordifferent and are each independently selected from the group consistingof hydrogen, deuterium, a halogen group, a nitrile group, a nitro group,an imide group, an amide group, a hydroxyl group, a substituted orunsubstituted alkyl group, a substituted or unsubstituted cycloalkylgroup, a substituted or unsubstituted alkoxy group, a substituted orunsubstituted aryloxy group, a substituted or unsubstituted alkylthioxygroup, a substituted or unsubstituted arylthioxy group, a substituted orunsubstituted alkylsulfoxy group, a substituted or unsubstitutedarylsulfoxy group, a substituted or unsubstituted alkenyl group, asubstituted or unsubstituted silyl group, a substituted or unsubstitutedboron group, a substituted or unsubstituted alkylamine group, asubstituted or unsubstituted aralkylamine group, a substituted orunsubstituted arylamine group, a substituted or unsubstitutedheteroarylamine group, a substituted or unsubstituted aryl group, asubstituted or unsubstituted fluorenyl group, a substituted orunsubstituted carbazole group, and a substituted or unsubstitutedheterocyclic group containing at least one heteroatom selected fromamong N, O and S, or adjacent two of R_(a), R_(b) and R₆ to R₁₁ may forma condensed ring.
 13. The copolymer of claim 12, wherein the first unitis present in an amount of greater than 0 mole % and 10 mole % or lessbased on the total moles of monomers constituting the polymer, thesecond unit is present in an amount of greater than 0 mole % and 50 mole% or less based on the total moles of the monomers, and the third unitis present in an amount of more than 0 mole % and 40 mole % or lessbased on the total moles of the monomers.
 14. The copolymer of claim 1,wherein the copolymer is represented by the following formula 5:

wherein R₁, R_(a), R_(b), o and p are as defined in formula 1; q and rare each an integer ranging from 0 to 3; s and t are each an integerranging from 0 to 4; l is a mole fraction in the range of 0<l≦1; m is amole fraction in the range of 0≦m<1; l+m=1; n is an integer ranging from1 to 10,000; R″ are the same or different and are each independentlyselected from the group consisting of hydrogen, deuterium, a halogengroup, a nitrile group, a nitro group, an imide group, an amide group, ahydroxyl group, a substituted or unsubstituted alkyl group, asubstituted or unsubstituted cycloalkyl group, a substituted orunsubstituted alkoxy group, a substituted or unsubstituted aryloxygroup, a substituted or unsubstituted alkylthioxy group, a substitutedor unsubstituted arylthioxy group, a substituted or unsubstitutedalkylsulfoxy group, a substituted or unsubstituted arylsulfoxy group, asubstituted or unsubstituted alkenyl group, a substituted orunsubstituted silyl group, a substituted or unsubstituted boron group, asubstituted or unsubstituted alkylamine group, a substituted orunsubstituted aralkylamine group, a substituted or unsubstitutedarylamine group, a substituted or unsubstituted heteroarylamine group, asubstituted or unsubstituted aryl group, a substituted or unsubstitutedfluorenyl group, a substituted or unsubstituted carbazole group, and asubstituted or unsubstituted heterocyclic group containing at least oneheteroatom selected from among N, O and S; and R₆ to R₁₁ are the same ordifferent and are each independently selected from the group consistingof hydrogen, deuterium, a halogen group, a nitrile group, a nitro group,an imide group, an amide group, a hydroxyl group, a substituted orunsubstituted alkyl group, a substituted or unsubstituted cycloalkylgroup, a substituted or unsubstituted alkoxy group, a substituted orunsubstituted aryloxy group, a substituted or unsubstituted alkylthioxygroup, a substituted or unsubstituted arylthioxy group, a substituted orunsubstituted alkylsulfoxy group, a substituted or unsubstitutedarylsulfoxy group, a substituted or unsubstituted alkenyl group, asubstituted or unsubstituted silyl group, a substituted or unsubstitutedboron group, a substituted or unsubstituted alkylamine group, asubstituted or unsubstituted aralkylamine group, a substituted orunsubstituted arylamine group, a substituted or unsubstitutedheteroarylamine group, a substituted or unsubstituted aryl group, asubstituted or unsubstituted fluorenyl group, a substituted orunsubstituted carbazole group, and a substituted or unsubstitutedheterocyclic group containing at least one heteroatom selected fromamong N, O and S, or adjacent two of R₆ to R₁₁ may form a condensedring.
 15. The copolymer of claim 1, wherein the copolymer furthercomprises a fourth unit represented by the following formula 6 and afifth unit represented by the following formula 7:

wherein R₁ is as defined in formula 1; l is a mole fraction in the rangeof 0<l≦1; m is a mole fraction in the range of 0≦m<1; l+m=1; and R″ isselected from the group consisting of hydrogen, deuterium, a halogengroup, a nitrile group, a nitro group, an imide group, an amide group, ahydroxyl group, a substituted or unsubstituted alkyl group, asubstituted or unsubstituted cycloalkyl group, a substituted orunsubstituted alkoxy group, a substituted or unsubstituted aryloxygroup, a substituted or unsubstituted alkylthioxy group, a substitutedor unsubstituted arylthioxy group, a substituted or unsubstitutedalkylsulfoxy group, a substituted or unsubstituted arylsulfoxy group, asubstituted or unsubstituted alkenyl group, a substituted orunsubstituted silyl group, a substituted or unsubstituted boron group, asubstituted or unsubstituted alkylamine group, a substituted orunsubstituted aralkylamine group, a substituted or unsubstitutedarylamine group, a substituted or unsubstituted heteroarylamine group, asubstituted or unsubstituted aryl group, a substituted or unsubstitutedfluorenyl group, a substituted or unsubstituted carbazole group, and asubstituted or unsubstituted heterocyclic group containing at least oneheteroatom selected from among N, O and S.
 16. The copolymer of claim 1,wherein the copolymer has an aryl group as its end group.
 17. Thecopolymer of claim 1, wherein the copolymer has a heterocyclic group asits end group.
 18. The copolymer of claim 1, wherein the copolymer has anumber-average molecular weight of 500-1,000,000 g/mol.
 19. Thecopolymer of claim 1, wherein the copolymer has a molecular weightdistribution of 1-100.
 20. An organic solar cell comprising: a firstelectrode; a second electrode opposite the first electrode; and one ormore organic material layers interposed between the first electrode andthe second electrode and including a photoactive layer, wherein one ormore of the organic material layers comprise the copolymer of claim 1.21. The organic solar cell of claim 20, wherein the organic materiallayers comprise one or more selected from the group consisting of anelectron donor and an electron acceptor, wherein the electron donor isthe copolymer.
 22. The organic solar cell of claim 21, wherein theelectron acceptor is selected from the group consisting of fullerene,fullerene derivatives, carbon nanotubes, carbon nanotube derivatives,vasocuproin, semiconductor elements, semiconductor compounds, andcombinations thereof.
 23. The organic solar cell of claim 21, whereinthe electron acceptor is a C60 fullerene derivative or a C70 fullerenederivative.
 24. The organic solar cell of claim 21, wherein thecopolymer and the electron acceptor are mixed with each other at aweight ratio of 1:0.5-1:4.
 25. The organic solar cell of claim 23,wherein the polymer and the C60 fullerene derivative or the C70fullerene derivative are mixed with each other at a weight ratio of1:0.5-1:4.
 26. A method for fabricating an organic solar cell, themethod comprising the steps of: preparing a substrate; forming a firstelectrode on a region of rear sides of the substrate; forming on thefirst electrode an organic material layer comprising the copolymer ofclaim 1; and forming a second electrode on the organic material layer.